China on Wednesday marks the 80th anniversary of the Nanjing massacre by Japanese troops, an enduring source of bad blood as present-day rivalry between the two countries keeps a spotlight on historical animosities.
Top leaders will preside over memorial services in the eastern city, Beijing says, but it is yet to confirm whether President Xi Jinping will lend weight to the occasion by attending.
According to China some 300,000 civilians and soldiers were killed in a frenzy of murder, torture, rape, arson and looting in the six weeks after the invading Japanese military entered Nanjing, then the capital city, on December 13, 1937.
It remains one of the most fraught anniversaries for the two powerful neighbours due to stubborn disputes over the toll and periodic denials by Japanese arch-conservatives that the episode took place.
Many in China say this symbolises Japan's unwillingness to completely atone for its wartime aggression.
Officially, Japan concedes that "the killing of a large number of noncombatants, looting and other acts occurred" but says it is "difficult" to determine precise figures.
The issue receded during the Cold War but has re-emerged as China strikes an increasingly muscular stance under Xi, while critics say Japanese revisionists have grown bolder with conservative leader Shinzo Abe.
China in 2014 formally made the anniversary a National Day of Remembrance, effectively raising its profile.
Liang Yunxiang, an international relations expert at Peking University, said Beijing wants to keep such memories alive as leverage against Japan in modern-day disputes such as maritime territorial squabbles.
"There are current conflicts between the two countries, so historical issues are re-emerging. All history is contemporary," said Liang Yunxiang, an international relations expert at Peking University.
"Japan thinks these historical issues should have ended but China keeps hammering them as it becomes more powerful."
Commemorations will centre on the sombre and poignant memorial hall and museum in Nanjing, but observances are expected elsewhere throughout China as well.
Beijing has said little about the anniversary, but a Chinese group this week reiterated its annual demand for Japan to compensate relatives of victims.
Fewer than 100 people designated as massacre "survivors" remain alive, however, and both sides have repeatedly expressed a desire to look forward and avoiding rocking their huge trade relationship.
But the spectre of Japanese aggression refuses to completely fade away.
Abe, the grandson of a wartime minister, has been accused of trying to gloss over it.
In 2015, he expressed "deep remorse" for Japan's actions in Asia, but also said future Japanese generations need not continually apologise, drawing criticism in China and South Korea, another wartime victim.
Japanese politicians also have repeatedly angered Asian neighbours by visiting Tokyo's Yasukuni Shrine, which commemorates Japan's military dead including convicted war criminals.
China's Nanjing toll is disputed even by some western academics who put it as low as the tens of thousands, but no respected historians dispute that a massacre occurred.
In 2014, Xi marked the first National Remembrance Day with a speech in Nanjing saying the slaughter and its "300,000 deceased victims" could not be denied.
Japan invaded China in the 1930s and they fought a full-scale war between 1937 and 1945, until Japan's defeat in World War II.
China suffered immense loss of life, reserving special anger over a sense that Japan, unlike Germany, has never properly atoned.
Relations plunged in 2005 as China was swept by rare anti-Japan protests denouncing its war conduct.
But analysts say China's stability-obsessed leaders are deeply fearful of letting such passions re-emerge and potentially spiral out of control.